For Part A) multiply the radius (28) by two in order to get the diameter. Take that product and multiply it by the "abbreviation" of pi that they give you (3.14). BAM, you get the circumference of the circle.
Part B) Because you're covering something, you need to find the area rather than the circumference (the distance around a circle). It's like needing to know the number of square units that can fit on a wall to figure out how many gallons of paint you need to cover it entirely.
Part C) Circumference, just I said.. the key word here is around. Distance around a circle !!